1. Field of the Invention
This invention relates to an anti-vibration device.
2. Description of the Related Art
For anti-vibration devices for supporting and fixing an automotive engine or transmission so as not to transmit vibrations of the engine, etc. to the vehicle body frame, a hydraulic type anti-vibration device is, for example, known.
A typical hydraulic anti-vibration device is, in general, made up of a first fitting to be mounted on an engine side, a second fitting to be mounted on a vehicle body frame side, a vibration isolating base made of rubber-like elastomer interconnecting both, a diaphragm attached to the second fitting, and a liquid-sealed chamber defined between the diaphragm and the vibration-isolating base. The liquid-sealed chamber is separated by a partition member into a first liquid chamber on the vibration isolating base side and a second liquid chamber on the diaphragm side, both the first and second liquid chambers communicating with each other through an orifice. Among such liquid-filled anti-vibration devices, the one having a stirring plate disposed rigidly to a mounting end of the first fitting within the first liquid chamber is known.
According to this hydraulic anti-vibration device, a liquid fluidization effect (resonance action) between the first and the second liquid chambers by the orifice and a vibration deadening effect of the vibration-isolating base permit to perform a vibration damping function and a vibration insulating function. Further it is also possible to resonate the liquid passing through the orifice defined between an outer peripheral edge of the stirring plate and an inner peripheral surface of the first liquid chamber (the vibration isolating base) in a high frequency region, to exhibit a low dynamic spring constant in the high frequency region.
A conventional expedient for fixing the stirring plate to a mounting end piece of a first fitting is disclosed in JP Patent Application Publication No. 2000-346120 A. According to this Reference, the mounting end piece of the first fitting is inserted in a mounting hole of the stirring plate, with one plate surface thereof received on a stepped portion formed on the mounting end piece; a projecting portion of the mounting end piece protruding out of the mounting hole is crushed in a riveted form and brought into pressure contact with the other plate surface of the stirring plate, whereby the stirring plate is fixed to the mounting end piece.
In recent years a reduction in weight of hydraulic anti-vibration devices is requested, and a current trend is that the first fitting is formed with a metal such as aluminum diecast. In the case where the first fitting is thus formed with diecast aluminum or the like metal, because of brittleness of the first fitting, a problem arose in that when the projecting portion was crushed in a rivet form by means of a pressing tool according to the conventional fixing expedient, an overhang part of the projecting portion (an overhang of the rivet head) being in pressure contact with the aforesaid other surface of the stirring plate was fractured.
Further problem was that even if the overhang part was not collapsed when crushed, after the stirring plate was assembled together with other members into the hydraulic anti-vibration device, the overhang of the projecting portion being in press contact with the other surface of the stirring plate was collapsed because of shortage of strength and the stirring plate came off from the first fitting.